1. Field of the Invention
The present invention relates to a fixing device that fixes a toner image transferred onto a recording sheet on the recording sheet and an image forming apparatus equipped with the same.
2. Description of the Related Art
There has been known a fixing device used in an image forming apparatus, such as a printer and a copying machine, for fixing a toner image transferred onto a recording sheet on the recording sheet. Such a fixing device adopts means by which an elastic layer (rubber layer) is provided to a pressure (press) roller and a fixing (heat) roller, so that a recording sheet is separated from the circumferential surface of the fixing roller by a nip shape formed by the pressure roller and the fixing roller.
In a case where the elastic layer is provided to the fixing roller, however, the low thermal conductivity of the elastic layer causes inconveniences, such as deterioration in the characteristics of temperature following during a continuous sheet passing operation and an extension of the warm-up time, which makes it difficult to reach a satisfactory level to respond to the trend toward energy conservation in recent years. A technique of fixing a toner image on a recording sheet with the use of a belt has been proposed and is now adopted in commercially available products. This technique, however, makes the structure complex and has an inconvenience that the cost is increased.
Meanwhile, there is known a fixing device that uses, as the fixing roller, a so-called hard roller formed by covering the surface of the cored bar made of aluminum or iron with a coating or a tube of fluorocarbon resin. This fixing device is able to shorten the warm-up time sufficiently owing to the high thermal conductivity of the fixing roller, and the fixing device can be manufactured at a low cost.
In a case where the fixing (hard) roller described above is used, however, a high adhesion force develops between the fixing roller and a recording sheet where a large amount of fused toner particles are present. It is therefore necessary to use means for forcedly separating a recording sheet from the circumferential surface of the fixing roller by bringing a separation claw into contact with the fixing roller. In this case, the occurrence of sheet jamming caused by the separation claw has to be suppressed to the extent possible.